Fix typechecking issue with Python 3.10

[davide125]

What:

Fix a typechecking error when building TestSlide on Python 3.10 that was found in Fedora (https://bugzilla.redhat.com/show_bug.cgi?id=1981718).

Why:

testslide/runner.py:288: error: Incompatible types in assignment (expression has type "BaseException", variable has type "Union[Exception, AggregatedExceptions]")
Found 1 error in 1 file (checked 26 source files)
make: *** [Makefile:87: mypy] Error 1

How:

Adding the missing type

Risks:

It's typechecking

Checklist:

• Added tests, if you've added code that should be tested N/A
• Updated the documentation, if you've changed APIs N/A
• Ensured the test suite passes
• Made sure your code lints
• Completed the Contributor License Agreement ("CLA")

[deathowl]

Thanks, as a follow up i'll add 3.10 to the build matrix. And I'll import this PR

[facebook-github-bot]

@deathowl has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[coveralls]

Pull Request Test Coverage Report for Build 1026915321

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 94.181%

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Totals
Change from base Build 953161056:	0.0%
Covered Lines:	2606
Relevant Lines:	2767

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💛 - Coveralls

[facebook-github-bot]

@deathowl merged this pull request in 8b0c16c.